Herpes simplex virus (HSV) is a major cause of sexually transmitted disease. The disease can be controlled to some extent with antiviral drugs but not yet prevented or cured. The overall goal of this project is to define the molecular interactions required for HSV to infect cells of the female genital tract and to spread to cells of the nervous system, with a focus on viral ligands and cell receptors that mediate HSV type 2 (HSV-2) entry into human and mouse cells. Besides heparan sulfate, which can serve as a binding receptor for virus, the two most efficient entry receptors for HSV-2 are HVEM and nectin-1, both for mice and for humans. Thus, receptor-dependent aspects of pathogenesis in mice are likely to be relevant to humans. The ligands for heparan sulfate are viral gB and gC, the latter of which also binds the C3b component of complement and protects virus from neutralization by complement. Viral gD is the ligand for HVEM and nectin-1. It is our hypothesis that HSV uses different receptors to enter different cell types and that inability of the virus (due to mutation or natural polymorphism) to use a particular entry receptor can either prevent infection or change the course of disease. This hypothesis will be tested in a mouse model of disease resulting from virus inoculation via the vagina and in primary cells cultured from the mouse and human female genital tracts. The specific aims are to determine (1) whether the disease course in mice and spectrum of cells infected are altered by mutations of the mice that abrogate HVEM or nectin-1 expression or by mutations in HSV-2 that prevent viral entry via HVEM or nectin-1 or that alter interactions with heparan sulfate and complement; (2) whether mice that survive infection with an attenuated HSV-2 mutant escape latent infection but exhibit resistance to challenge with wild-type HSV-2 and (3) whether the HSV-2 mutants have altered ability to infect cells cultured from the female genital tracts of mice and humans and whether complement influences viral infectivity. This project focuses on the central theme of the center, namely acquisition, pathogenesis and prevention of STIs in women. Results obtained will identify interactions that must be blocked to prevent HSV infect on and will address the feasibility of a non-neurotropic live HSV vaccine.